Natural gas and liquefied petroleum gas are typically recovered by drilling wells in the crust of the earth, with the wells passing through water tables and moist rock. As the gas is pumped out of the earth it normally becomes saturated with water so that the gas may be saturated with as much as 100% water humidity. Because the gas contains so much water it is necessary to remove the water as it tends to freeze in the winter and is considered a contaminant of the gas. The removal of the water from the gas is typically achieved by passing the gas through a triethylene glycol system which removes nearly all of the water from the gas. In fact, generally, the water in the gas is reduced down to around 4 to 10 pounds of water per one million cubic feet of gas, which is considered dehydrated or water under-saturated. Also, gas having from around 4 to 10 pounds of water per one million cubic feet of gas is considered non-contaminated and acceptable for commercial use.
When gas is treated to remove sulfur it is normally passed through a reactor vessel containing iron oxide or other types of metal oxides, which react with and remove the sulfur from the gas. However, in order for the iron oxide to effectively react with and remove the sulfur from the gas, the iron oxide must be kept moist. If the iron oxide is allowed to dry out, sulfur removal will be ineffective and the period of time for removal may be too long. Water or non-aqueous liquids can be used to moisten the iron oxide. Water, however, is usually the liquid which is used to keep the iron oxide moist, in part because water increases the reactivity of the iron oxide. Additionally, water is usually added to the gas before it is passed through the iron oxide bed to keep the iron oxide bed from drying out and to maintain the high reactivity of the iron oxide bed. It should be noted that if the gas is dehydrated when it is passed into an iron oxide bed that has been moistened with water, the water will migrate into the gas changing the gas from dehydrated to hydrated. Consequently, under traditional sulfur removal systems, gas which passes through the sulfur removal process tends to become or remain hydrated with water.
As a result, once the sulfur has been removed from the gas it must further be treated to remove the water from the gas, which is disadvantageous because another step is added to the process. Also, typically an additional step is involved in moisturizing the gas prior to entry into the reactor vessel. The additional steps can be costly and time consuming.
As mentioned, non-aqueous solutions may be used to moisten the metal oxide composition; however, non-aqueous solutions, other than glycols or hygroscopic agents, suffer from some disadvantages. The non-aqueous solutions tend to evaporate quickly. Also, most of the non-aqueous solutions are not hygroscopic which means they do not readily attract water from the gas being treated.
Thus, as can be seen, the use of water to moisten metal oxide beds is disadvantageous. Because water is disadvantageous, it would be desirable to have a method and composition which could treat dehydrated gas so as to eliminate the gas moistening step prior to sulfur removal. It would further be desirable to have a composition and method which does not contribute substantial amounts of water to the gas being treated. Finally, it is desirable to have a method that eliminates the step of removing water from gas after the removal of the sulfur from the gas.